Thermostat



OC 22, 1963 K J. LINGNAU 3,107,532

THERMOSTAT Filed April 16, 1962 Jn venfar: josef zing/Tau Unted States Patent O 3,107,532 THERMOSTAT Josef Lingnau, Bremen-Borgfeld, Germany, assigner to Gustav F. Gerrits KG., Bremen, Germany a corporation of Germany Filed Apr. 16, 1962, Ser. No. 137,518 Claims priority, application Germany Apr. i4, 1961 14 Claims. (Cl. 'i3-363.1)

This invention relates to a thermostat and refers more particularly to a thermostat consisting of at least one pair of birnetallic discs which are curved in opposite directions and loosely mounted one over the other.

Thermostats consisting of individual bimetallic discs loosely mounted in rows upon one or more guide rods, are generally well known and are used wherever regulation and guiding are to be carried out by means of ternperatune variations. These individual discs, which may be combined into a bi-rnetallic column, have, however, the draw'back that in their curved operative condition they rarely lie properly directly concentrically one over the other, since the contacting edges of the individual pairs of elements do not constitute an adequate supporting surface, so thatrthe discs slide inwardly or outwardly between the guiding rod and the disc bore, depending upon the extent of play. In most cases pairs of discs can support each other only upon a portion ci their circumference.

The result is that there is clamping or edge locking between the rod and the bimetallic discs, so that proper operation of the thermostat is jeopardized. Furthermore, a direct consequence of this condition consists in variations in the length of stroke, so that these thermostats can be used only in locations wherein no uniform precise operations are required. Finally, the irregular engagements of the discs at the contacting edges produce'in time dislocations and form changes in the discs, which contribute to further irregularities.

Furthermore, thermostats which are preferably used in steam plants and the like, particularly for thermically operated dischargers of condensation water, wherein they are subjected to the attack of corrosion-producing media, such as steam, condensate and their respective chemical impurities must be constructed with special care so as to assure durability and an `operating power which must remain constant.

For example, it is known in prior art to use austenite and `ferrite steels to provide the greatest possible operational stroke.

However, these known bimetals do not possess the necessary resistance to corrosion and heat for use in steam installations or the like, wherein there are flows of acid or alkali reacting media and which are subjected to high temperatures.

Up to now, the problem of making a bimetal which has adequate ybending capacity and lwhich is secure against corrosion, was not solved satisfactorily, since in the case 'of a corrosion-resisting element its bending capacity was too small, while when the bending capacity was great, there was no adequate resistance against corrosion.

For that reason bimetals were often used which were made resistant against corrosion by means of surface coatings which were applied galvanically by known methods. However, this protective `coating is soon dissolved, since the layers are quickly affected by the attacking medium. Furthermore, these bimetals poorly resist mechanical stresses, so that the life of the bimetal is not .prolonged to any substantial extent by the provision of a protective coating.

An object `of the present invention is to effectively elimilCe nate these drawbacks of prior art constructions by the simplest possible means.

Other objects of the present invention will become apparent in the course of the following specification.

In accomplishing the objects of the present invention it was found desirable to form each pair of bimetallic discs constituting a column, out of discs of different sizes in such manner that the circumferential edge of the smaller disc is supported upon the inner surface of the larger disc.

The result of this l*feature of the present invention is that perfect engagement is provided whenever the two individual discs support one another, since due to the difference in size the smaller disc must necessarily lie upon the inner surface of the larger disc. As compared to prior art devices, this advantage of the construction of the present invention is combined with the further feature that the smaller discs are centered automatically upon the concave inner surfaces of the larger discs during the bending process, so that operational diliiculties resulting from clamping or edge locking between the guide rod and the discs are eliminated and so that there is always the same stroke length at the same temperature.

In accordance with the present invention, the individual discs of each pair can have different outer shapes. it was found as a part of the present invention, that it is particularly advantageous, when only one guide rod is used, to combine a preferably circular disc with an angular disc, whereby the angular disc should he preferably the smaller one. Due to this arrangement the loss in the stroke length of the smaller disc is balanced out again since, as was determined in actual practice, the free edges of an angular disc are lbent particularly strongly. lt is possible to retain the generally employed central rod guide despite the use of different discs, since in view of the size dilerences, the smaller angular disc can be supported upon the larger round disc in each position.

According to a further development of the present invention7 the automatic centering of the 'discs is facilitated by rounding ott at least the supporting edges of the smaller dise, thereby also increasing its sliding capacity. This rounding of the edges is particularly effective when the edge of the smaller disc and the edge surface of the larger Idisc serving as the support, are hardened or provided with a hard chromium coating. This feature does not only provide a further improvement in the sliding capacity, ibut as its result the highly stressed engaging zones of the individual discs acquire considerably greater resistance against wear and tear.

Extensive experiments ywith non-corresion-resistant nickel steels have demonstrated that the attack by corrosion becomes excessive only when these steels are subjected to moving media, such as steam or condensation water. Surprisingly, it was discovered that when the medium is in state of rest, the attack by corrosion proceeds so slowly that these steels have a durability which is a substantial multiple of that prevailing `during their use in a moving medium. This phenomenon can be explained by the fact that a neutralizing process takes place between the metallic layer and the boundary layer of the medium, whereby this process acts to prevent corrosion.

According to a further embodiment or" the present invention, this discovery is used to eliminate the above indicated drawbacks in such heat-expanding bodies which are exposed to moving steam or condensation water, as is, for example, the case with dischargers of condensation water. rTherefore, the bimetal'component with great heat expansion is exposed to the moving portion of the medium and consists of corrosion-resistant steel, preferably austenitic it/8% chromium-nickel steel, while the other component which cornes into contact with the non- .from turning.

moving part of the medium, consists of a non-corrosionresistant steel having smaller heat expansion, preferably Invar steel with about 30-36% nickel.

This feature malces it possible to provide bimetatllic expansion bodies which., 'on the one hand, have exceptionally ygreat strokes as the result of the connection of composite steels with heat expansion -coecients 18 10- and to bimetals, and which on the other hand, by maintaining the component rnade of non-conrosion-resistant Invar steel with heat expansion coeiiicient 0 away from Y the moving medium and keeping it in contact only with a quiet medium, have such ya delayed corrosion eliect due to the neutralization appearing at the borderzo-nes between the ymedium and the metal, that their durability `will be entirely adequate and will not be substantially less than that `of lb-imretals made of non-rusting steel. l

By the use of [discs of `diffe-rent size but of circular outline, whereby the edge of the smaller disc is supported upon the inner surface of the larger disc, such a good sealing at the edges is attained, that the thermostat when heated forms one or more hollow chambers containing the medium at rest and surrounded by the flowing medium, the inner walls of the hollow chambers consisting of a non-corrosion-resistant steel.

Obviously, the ibimetallic discs can alsof consist of an austenitic steel component and a ferritic steel component, whereby both components are non-rusting steels, the two bimetallic components being joined into ya |bimetalxlic body by spot welding, roll seam welding or application welding.

According to the present invention, it is advantageous to use an austenitic 18/ 8 chromium-nickel steel for the component having the llarge-r expansion and an about 13 chromium steel for the component with the smaller ex- 'pansion The invention will appear more clearly from the following detailed 'description when taken `in connection with the accompanying drawing showing, by way of example, preferred embodiments of the inventive idea.

In the drawing:

FIGURE 1 is la section through two pairs of discs mounted upon a central shaft and constructed in accord-` ance with the present invention.

.FIGURE 2 is atop view of `the device shown in FIG. 1.

vFIGURE 3 shows in tot l View a differently constructed embodiment of the present invention wherein differently nvention. l y

FIGURE 7 is an enlarged section through hard-chromed edge portions of twlofdiscs of a pair.

The pairs of idiscs` shown in FIGS. l and 2 consistl of individual discs l andY 2 are different in size Vand which are mounted in a row upon a central guiding rod 3.' The discs -1 of each pair are smaller in diameter, so that in their curved operational condition their edges 4 can be circumterentially supported upon the inner surfaces 5 ofthe larger discs 2, thus providing Van excellent sealing of fthe inner hollow space. n

The construction of FIGURE 3 is different from that of FIGS. :l iand 2 only in that the smaller disc 1a which is supported by the larger disc 2, is angular in shape and is provided with lbr-oken oli corners 6. The discs 1ra and f2 Aare mounted upon the rod 31.

Y FIGURES `4 and 5 show a construction wherein both discs lb and 2b are angular in shape with parallel edges in stepped formation. Two guide pinsS and 9 located on lboth sides ofthe guiding member 3 and extending through the superposed discs, Iare used to prevent them [It not essential that the bimetallic column be mounted in the 'manner' shown in FIG. l. As illustrated in FIG- ment of discs constructed in accordance with the present v URE 6, it is obviously possible to mount the individual discs l and 2 one over the other alternately asto size,

so that two equally large discsof two disc pairs will always lie one directly over the other.

To save the edges of the smaller ydiscs 1c (FIG. 7) as well as the edge surfaces 5a of the larger ydiscs 2c from excessive wear and tear caused by friction, the frictionally exposed edges of the discs lc are provided with a hard chromium coating l0, while the edge surfaces 5a of the larger :discs 2c are provided with a hard chromium coating lila. These coatings also increase the sliding capacity of the contacting parts.

Obviously, wear and tear can 'be also diminished by other means, for example, lby hardening the contacting parts. f v

` FGURE 7 shows that the edge 'of the smaller disc 1c is rounded at ll sol #as to further increase the sliding capacity of the parts, with the result that yduring stroke movements the discs are substantially automatically centered relatively to each other. Furthermore, the rounded edges lll further decrease wear and tear and prevent the possibility of a sharp edge of the Ismaller disc damaging after a while the larger disc.

The positions of disc pai-rs shown in FIGS. 1, 4 and 6 can be their positions of rest or their operative positions, depending upon the size, arrangement and selection of material of the individual bimetallic components of each disc. For example, the drawing showing the discs as curving in opposite idirections may show them in their operative positions while they are under theinlluence of heat, while when cooled the `discs vvcanbe flat or only slightly curved. VA reverse construction is also possible,

namely, discs can be used which are curved when cool and which assume a hat shape when heated.

As shown in the drawing, the diameter or the largest distance between opposed edges of the larger disc is greater than the diameter or the largest Idistance between the edges of the smaller disc by a length which is at least twice the size of play between the guiding rod 3 and the edges of the openings through which the guiding rod 3 extends.

It is apparent that the above-described examples have been given solely by way of illustration and not by way of limitation and that they are sub-ject to many variations and modiications within the scope of the present invention. All such variations and modifications are to be included within the scope of the present invention.

What is claimed is:

l. A thermostat comprising at least one pair of bimetallic [discs curving in opposite directions and loosely mounted one over the other, said two'discs being of dilerent size,v the edges of the disc of smaller size being supported by the inner surface of the disc of larger size.

2. A thermostat in `accordance with claim l, comprising a guide member extending through openings formed in the discs, the largest .distance between opposed edges of the langer disc being greater than the largest distance between opposed edges `of the smaller disc by a length which is at least twice the size of Aplay between said guide member and said openings. i Y

Y 3. A thermostat in accordance with claim l, wherein said edges of the ldisc of smal-ler size are rounded.

4. A thermostat in accordance with claim 1, wherein the two discs are of different shape 5. A thermostat in accordance with claim'4, wherein the disc of larger size is round.

6. A thermostat comprising iat least one pair of bimetallic discs curving in opposite directions and loosely mounted one over the other, said two discs beingof differentsize, the edges of the disc of smaller size being sup-r ported bythe inner surface of the disc of larger size, said edges'rlbeing hardened. v Y 7. A thermostat comprising at least one pair of bimetal- Y discs curving in opposite directions and loosely mounted one over the-other, said two discs being of different size,

5 the inner surface of the dise of larger size, and a hard chromium coating over said edges.

8. A thermostat comprising at least one pair of birnetallic discs curving in opposite directions yand loosely mounted one over the other, said ytwo discs being of different size, the edges of the disc of smaller' size being supported by the inner surface of the disc of larger size, the portion of the inner surface supporting said edges being hardened.

9. A tneiirnostat comprising atleast one pair of bimetallic discs curving in `opposite directions and loosely mounted one over the other, said 4two discs being of different size, the edges of the disc of smaller size being supported by the inner surface of the ldisc of larger size, and a hard chromium coating over the portion of the inner surface supporting said edges.

ll0. A thermostat, particularly for armatu'es exposed to flowing `gases or liquids, said thermostat comprising at least one pair of bimetallic discs curving in opposite directions #and loosely mounted one over the other, said two discs being of dierent size, the edges of the disc of smaller size being .supported by the inner surface of the disc of larger size, one bimetaliic component of each `disc consisting of vaustenitic steel `and the other birnetellic component of the same `disc consisting of ferritic steel, the two coniponents being Iron-rustiinb7 steels joined by welding.

l1. A themrnostat in accordance with claim 10, wherein said one component consists of Ian l18/8 chromium-nickel steel and said other component consists of a substantially 13% chromium steel.

l2. A thermostat Aadapted to be exposed to owing fluids, said thermostat comprising et least one pair of round bimetallic discs curving in opposite directions and loosely mounted one over the other, said two discs being of different size, the edges of tile disc of smaller size being supported lby `the inner surface or .e disc of larger size, whereby ian inner chamber is formed between ythe two discs, the `outer surfaces of said `discs being exposed to a flowing fluid while said inner chamber is adopted to contain said uid in condition `of rest, one bimetaillic compone-nt of each ydisc which is exposed `to the ilo-Wing iluid -iiaving `a comparatively larger heat expansion coei'licient and consisting of corrosionresisting steel, the other bi- Lmetallic component of le same steel 4which is exposed to the iiuid in condition of rest having a comparatively smaller `beat expansion coeilcient and consisting of noncorrosion-resisting steel.

13. A thermostat in `accordance with claim l2, wherein said corrosion-resisting steel consists of austenitic 18/8 chromium-nickel steel.

i4. A thermostat in `accordance with claim l2, wherein non-corrosion-resisting steel consists of inval steel with substantially Btl-36% nickel.

No references cited. 

1. A THERMOSTAT COMPRISING AT LEAST ONE PAIR OF BIMETALLIC DISCS CURVING IN OPPOSITE DIRECTIONS AND LOOSELY MOUNTED ONE OVER THE OTHER, SAID TWO DISCS BEING OF DIFFERENT SIZE, THE EDGES OF THE DISC OF SMALLER SIZE BEING SUPPORTED BY THE INNER SURFACE OF THE DISC OF LARGER SIZE. 